A known variable valve timing control device for an internal combustion engine is disclosed in Japanese Patent Laid-Open Publication No. 11-294121. The disclosed variable valve timing control device is provided in the drive train that transmits a drive force from a crankshaft of the internal combustion engine to a camshaft for opening and closing an exhaust valve of the combustion engine. The known variable valve timing control device includes a housing member rotating with the crankshaft and a vane member rotating with the camshaft and accommodated in a receiving space formed within the housing member so as to rotate relative to the housing member within a predetermined angle. The variable valve timing control device further includes a switching valve for controlling an operation oil supply to an advanced angle chamber defined in the receiving space by the vane member and which volume becomes larger as the vane portion is rotated in an advanced angle direction relative to the housing member by virtue of the supply of the operation oil, and a retarded angle chamber defined in the receiving space by the vane member and which volume becomes larger as the vane member is rotated in a retarded angle direction relative to the housing member by virtue of the supply of the operation oil. Furthermore, the variable valve timing control device includes an oil pump for generating the operation oil, and a torsion spring for biasing the vane member to the advanced angle side (i.e., the direction that enlarges the advanced angle chamber) relative to the housing member. The biasing force of the torsion spring is set higher than or equal to an average torque of the camshaft at idling of the combustion engine under a high oil temperature for ensuring restarting performance of the engine.
According to the above-mentioned variable valve timing control device, if the engine is stopped irregularly under a low oil temperature, the biasing force of the torsion spring may become under the average torque of the camshaft due to a high viscosity of the operation oil. The engine cannot be sopped under the condition that the vane member is surely retained to the most advanced angle side. After the variable valve timing control device is stopped at any positions other than a most advanced angle phase (i.e., a phase of the camshaft is most advanced relative to the crank shaft) or an initial position, i.e. an intermediate angle phase positioned between the most advanced angle phase and a most retarded angle phase (i.e., the phase of the camshaft is most retarded relative to the crank shaft), a valve overlap period during which the exhaust valve and an intake valve are open at the same time is set longer when a sufficient oil is not generated by cranking rotations of the combustion engine for operating the variable valve timing control device for the exhaust valve at restarting of the combustion engine. Therefore, in the intake process, the exhaust gas inflows from the exhaust side and thus a new air-fuel mixture cannot inflows from the intake side. A stable ignition of the internal combustion engine is impossible, thereby enabling to start the internal combustion engine.
Thus, a need exists for an apparatus for controlling internal combustion engine equipped with a variable valve timing control device which can start the internal combustion engine even if the variable valve timing control device is stopped at a position other than the most advanced angle phase or the Intermediate angle phase.